Prior methods and apparatus for aligning teeth can be less than ideal in at least some instances. While braces can be used to move teeth into alignment, braces can be cumbersome to wear and can require expertise to place on the subject. Also, complex movements can be difficult to achieve and orthodontic placement may less than ideally address the complex movements of several teeth in at least some instances.
Transparent shell appliances have been used to successfully move teeth. For example a user can be provided with a series of transparent shell appliances. Each shell of the series of shells may correspond to a stage of the treatment. For example, a fourth shell in a series of ten shells may correspond to the fourth state of treatment. Although transparent shell appliances can be used to successfully reposition teeth, the transparent shell appliances can provide less than ideal results in at least some instances. For example, complex movements of teeth, such as to fill an extraction can be difficult to treat with transparent shell appliances. Also, in at least some instances, a wearer of a transparent shell appliance may not complete treatment, for example when teeth do not move sufficiently with the appliance and the user stops treatment. Additionally, in at least some instances, the course of treatment may need to be reevaluated as the treatment is implemented, which may necessitate the manufacture of a second series of transparent shell appliances, prolonging treatment time.
Prior methods and apparatus of aligning teeth with transparent shell appliances can rely on providing shells with cavities shaped to the tooth profile at a final intended position and orientation at a stage of the treatment. Work in relation to embodiments suggests cavities shaped to position a tooth at a final intended position and orientation at a stage of the treatment can provide less than ideal movement. Although attachments can be placed on teeth to facilitate movement of the teeth with polymeric shell appliances, the resulting movements can be less than ideal in at least some instances. For example, the force applied to the tooth can decrease as the tooth moves toward the target position. Also, the movement of a tooth may not be uniform, and the tooth may move more easily along some dimensions than others. For example, the movement of a tooth can occur along six degrees of freedom, and relative movement compared to a target movement can differ among the degrees of freedom of the tooth. Further, the movement of teeth can be coupled, such that movement of a first tooth can affect movement adjacent teeth.
Prior appliances to move teeth may provide teeth receiving cavities at locations corresponding to the locations of the teeth at the end of each stage of treatment. This approach can be less than ideal in at least some instances.
Although manufacturing appliances in accordance with target positions of the teeth at the end of each stage of treatment can be effective, work in relation to embodiments suggests that the amount of force applied to each tooth can be less than or greater than would be ideal, and the corresponding movement of the tooth can be less than ideal in at least some instances. There can be a discrepancy between the locations of the teeth receiving cavities of the polymeric shell appliance applied and current positions of the teeth. The force and moment may be created from the deformation of the polymeric shell appliance put on the teeth. When a tooth is moved close to its position in the next stage of the treatment course, the discrepancy between the polymeric shell appliance used and the tooth also can get smaller. Accordingly, the force applied by the polymeric shell appliance can be also reduced. When the force is small enough, there may be no tooth movement achieved until the next polymeric shell appliance with a new, larger discrepancy is used. Additionally, the force and moment created by the polymeric shell appliance can be from the discrepancy of the crown part of the tooth, and may be applied on tooth crown only, for example. However, the biological response for tooth movement can be generally centered on the tooth root and not the crown. Therefore, the force from the crown discrepancy may be less than ideal for root movement.
In light of the above, it would be desirable to provide improved methods and apparatus for moving teeth to target positions with polymeric shell appliances. Ideally such methods and apparatus would more accurately move teeth to target positions with decreased forces. In some embodiments, the methods, systems, and apparatus would allow dental practitioners to view, modify and approve suggested target tooth positions.